The aim of this research proposal is to generate pilot-scale chemical diversity libraries for their use in high throughput biological screening by the Molecular Libraries Screening Center Network (MLSCN). Our effort will be focused on development of diversity-oriented syntheses of bisheterocyclic libraries characterized by the presence of two heterocyclic moieties connected by a spacer. Both heterocyclic rings will be assembled in a combinatorial fashion during the synthesis. Individual library members will contain a combination of different heterocyclic rings thus providing access to classes of compounds so far not systematically studied, but with a substantial potential to become drugs. Proposed libraries are designed with subsequent optimization of initial hits in mind;synthetic routes allow introduction of a large selection of diverse building blocks for the synthesis of optimization libraries. Libraries will be prepared in combinatorial fashion on solid phase and library synthesis and logistic will not be tailored to any specific instrumentation;the synthesis will be compatible with any synthetic laboratory without requirement for any specific solid-phase instrumentation. Our long term objective is a systematic study of bisheterocyclic compounds using diversity-oriented combinatorial solid-phase synthesis and evaluating their biological activities in a broad range of screens. There are three specific aims of this project: 1. Library design and chemistry development: to design diverse bisheterocyclic library for subsequent combinatorial synthesis, to develop robust methodology for combinatorial solid-phase synthesis of selected compounds, and to assess the scope and limitation of the developed methodology for a diverse set of building blocks. 2. Library synthesis: to perform solid-phase combinatorial synthesis of a library containing 1000 compounds, using the directed split-and-pool methodology, followed by cleavage, isolation, purification, and full characterization of products. 3. Library submission: to format and organize compounds in a ready-to-test format according to the recommendation of the NIH Small-Molecule Repository and to prepare compound and reaction databases.